1. Field of the Invention
The present invention relates to microwave oscillators having very low phase noise and more particularly to an improved very low phase noise microwave oscillator having a reflection oscillator circuit operating in conjunction with a right-circular cylindrical waveguide cavity resonator.
2. Description of the Prior Art
Microwave oscillators with very low 1/f phase noise have numerous applications in microwave communication systems, radar systems, and elsewhere. Numerous attempts have been made to develop ultra low noise oscillators using a variety of different techniques and designs. The most recent attempts and the results achieved are reported in "GaAs: Key to Defense Electronics," by Edward Niehenke in the Microwave Journal, September 1985 issue at page 40. The very best FET designs have achieved phase noise figures between -95 and -105 dBc/Hz measured at 10 kHz from the main oscillator frequency which was in the 4 to 10 GHz frequency band.
Generally an oscillator with the lowest possible phase noise requires a resonator with the highest possible Q. Microwave cavity resonators have been known and used since the mid 1930's as resonant circuits for oscillators and filters because of their remarkably high Q and very high shunt impedance characteristics. The waveguide mode cavity resonator and particularly a right-circular cylindrical resonator is well suited to a low noise requirement since it has a large volume-to-surface area ratio (and thus has the potential for a high Q). Carefully designed silver or gold-plated right-circular cylindrical cavity resonators typically exhibit unloaded Q's well over 10000 in approximately the 6 to 8 GHz region, which is ideal for low noise oscillator circuits.
The subject invention is directed toward an improved low noise microwave oscillator design which exceeds the noise performance characteristics of existing oscillators.
Another object of the present invention is to provide an improved microwave cavity resonator which incorporates techniques for eliminating mode degeneracy which do not degrade the Q of the cavity.